1. Field of the Invention
The present invention pertains to telecommunications, and particularly the provision of multiple services supplied over an external network physical interface.
2. Related Art and other Considerations
It is now desirable to provide multiple services using a single telecommunications network. For example, differing services such as video, voice telephony, data, and other interactive and/or multimedia services can be carried together over a physical medium, e.g., an external network physical interface.
One example of such an external network physical interface capable of carrying integrated multiple services system is a hybrid fiber-coax (HFC) network. In a HFC network, a headend office receives signals from various sources (e.g., analog television, Internet access, digital video on-demand) and distributes an optical signal carrying these various signals to distribution centers or nodes. At the distribution centers the optical signal is converted and re-distributed to network interface units (NIU) or network terminals (NTs) which reside at customer premises. The network interface units receive the HFC signal using an internal transceiver (e.g., modem), and distribute the appropriate channels to televisions, personal computers, and telephones, etc.
Other types of external network physical interfaces are also emerging. Such other types of external network physical interfaces include, for example, Fiber-To-The-Home (FTTH) networks and Megabit-Speed Digital Subscriber Line (xDSL) networks. The xDSL networks employ dedicated telephone lines.
Apart from the type of external network physical interfaces, there is also the consideration of network protocol interface. One popular network protocol interface is Asynchronous Transfer Mode (ATM). ATM is a packet-oriented transfer mode which uses asynchronous time division multiplexing techniques. Packets are called cells and have a fixed size. An ATM cell consists of 53 octets, five of which form a header and forty eight of which constitute a "payload" or information portion of the cell. The header of the ATM cell includes two quantities which are used to identify a connection in an ATM network over which the cell is to travel, particularly the VPI (Virtual Path Identifier) and VCI (Virtual Channel Identifier). In general, the virtual is a principal path defined between two switching nodes of the network; the virtual channel is one specific connection on the respective principal path.
Many formats and interfaces for ATM technology have been standardized. For example, ATM has several "adaptation layers" which have been the subject of ITU standardization. In addition, an ATM interface known as "Utopia level 2" has been standardized, as set forth in The ATM Forum, Technical Committee, Utopia Level 2, Version 1.0, afphy-0039.000, June 1995.
In multi-service environments, the network interface units should be flexible for accommodating not only existing services, but additional other services and other types of external network physical interfaces as well.
Some network interface units use processor cores with complementary hardware blocks. For example, the Motorola 860SAR circuit has a control processor core, an SAR processor core which is customized to handle ATM SAR functions (e.g., AAL5), and an ethernet controller that handles ethernet functions.
Processor-based network interface units are flexible for the user because the user can easily modify the functionality by changing the software executed by the processor(s). However, processor-based network interface units also have disadvantages. One disadvantage is that main functionality has to be implemented in software by the user, which can be difficult and require extreme design effort. A second disadvantage is a limited data rate attainable with processor-based units. A third disadvantage is significant power consumption.
What is needed therefore, and an object of the present invention, is a predominately hardware-based network interface unit which is flexible and efficient.